Variable geometry mirror having high-precision, high geometry controllability

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable geometry cylinder mirror and more particularly to a highly configurable, high precision cylindrically deformable variable geometry mirror.

2. Description of the Related Art

In the field of high-precision micro optical systems such as an optical pickup, a micro variable focus mirror capable of changing the curvature of its reflecting face has been proposed so as to aim at simplification of the structure for focusing, which conventionally uses an electromagnetic actuator.

Further, in a small image pickup optical system, miniaturization is largely dependant on the size of the variable focus mirror.

Adoption of micro electromechanical system (MEMS) technology in a variable focus mirror enables low-cost, high-precision manufacturing thereof.

An example of the cylindrically deformable variable geometry cylinder mirror of this technology is a monolithic reflecting mirror apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402.

In this monolithic reflection mirror unit, as shown in

FIG. 26

, a metallic thin film

54

, which serves as an electrode layer, is formed on a silicon semiconductor substrate

51

, which acts as a fixed side electrode, through a silicon epitaxial layer

52

and a silicon oxide thin film

53

. Window holes

56

,

57

are formed in the silicon oxide thin film

53

and the metallic thin film

54

with a central portion

55

left between them.

Because the window holes

56

,

57

communicate with each other through a vacant portion

58

formed in the silicon epitaxial layer

52

, the central portion

55

is set up as a straddle-mounted type reflection mirror portion.

The straddle-mounted type reflection mirror portion

55

opposes the silicon semiconductor substrate

51

through the vacant portion

58

. By applying a potential difference to

51

and

55

, the reflection mirror portion

55

is distorted, thereby functioning as a variable geometry cylinder mirror.

However, although the variable geometry cylinder mirror employing the conventional monolithic type reflection mirror unit can be so constructed as a small, low-cost variable geometry cylinder mirror, the electrostatic force applied to the reflection mirror portion cannot be changed according to each position. Thus, this variable geometry cylinder mirror cannot be deformed to an asymmetrical shape.

Further, the variable geometry cylinder mirror using the conventional monolithic type reflection mirror unit can only be changed from a flat face to a concave face and it cannot be deformed to a convex shape.

Additionally, because the center of the reflection mirror portion always drops with deformation of the variable geometry cylinder mirror using the conventional monolithic type reflection mirror unit, there is a problem that the curvature cannot be changed with the center portion fixed.

Further, the straddle mounted type structure is distorted by deformation of the reflection mirror portion. Thus, if a large distortion is desired, a high voltage is needed in order to produce a large electrostatic force.

BRIEF SUMMARY OF THE INVENTION

The present invention has been achieved in view of the above-described problems and therefore, an object of the present invention is to provide a small variable geometry cylinder mirror, the shape of which can be freely set and can also be asymmetrical.

Another object of the present invention is to provide a variable geometry cylinder mirror, which can be deformed continuously from a concave face to a convex face and further which can be deformed with the center or any point of the reflection mirror fixed.

Still another object of the present invention is to provide a variable geometry cylinder mirror capable of obtaining large changes in curvature with a relatively low voltage.

In order achieve the above objects, according to a first aspect of the present invention, there is provided a variable geometry cylinder mirror comprising:

a frame member;

a flexible thin film in which two end portions opposing each other are supported by the frame member;

a reflection surface which is provided on the flexible thin film and reflects light;

a first electrode provided integrally with the flexible thin film;

a second electrode substantially fixed to the frame member so as to oppose the first electrode on an opposite side of the reflection surface; and

a third electrode substantially fixed to the frame member so as to oppose the first electrode on the same side as the reflection surface,

wherein an optical opening to introduce light into the reflection surface is provided on the side of the reflection surface,

at least any one of the second and third electrodes is divided in the direction connecting the two end portions, and

the configuration of the reflection surface is controlled to a desired configuration by applying a desired voltage selectively to between the first electrode and the divided second or third electrode.

According to a second aspect of the present invention, there is provided a variable geometry cylinder mirror according to the first aspect, wherein the reflection surface of the flexible thin film is formed of metallic thin film and serves as the first electrode.

According to a second aspect of the present invention, there is provided a variable geometry cylinder mirror according to first aspect, wherein an openings are provided on both sides of the reflection surface in the flexible member across a straight line connecting the end portions supported by the frame member.

According to a fourth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the first aspect, wherein in a region between the end portion supported by the frame member and the reflection surface in the flexible thin film, stiffness thereof in the direction in which the second or third electrode is divided is decreased.

According to a fifth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fourth, wherein the region in which the stiffness of the flexible thin film is dropped is wave-like.

According to a sixth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fifth aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and silicon nitride or metallic thin film and silicon oxide.

According to a seventh aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fourth aspect, wherein as for the sectional area of the flexible thin film in a direction perpendicular to the direction in which the second or third electrode is divided, that of the region in which the stiffness of the flexible thin film is dropped is smaller than that of a region corresponding to the reflection surface.

According to an eighth aspect of the present invention, there is provided variable geometry cylinder mirror according to the fourth aspect, wherein an opening or a cutout is provided in the region in which the stiffness of the flexible thin film is dropped.

According to a ninth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the first aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and polymer material thin film.

According to a tenth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the seventh aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and polymer material thin film.

According to an eleventh of the present invention, there is provided a variable geometry cylinder mirror according to the eighth aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and polymer material thin film.

According to a twelfth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the first aspect, wherein the third electrode and a supporting member thereof are provided outside the optical opening.

According to a thirteenth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the first aspect, wherein the third electrode is disposed within the optical opening while the third electrode disposed within the optical opening and the supporting member thereof have property allowing light to be transmitted through.

According to a fourteenth aspect of the present invention, there is provided a variable geometry cylinder mirror comprising:

a frame member;

a flexible thin film in which two end portions opposing each other are supported by the frame member;

a reflection surface which is provided on the flexible thin film and reflects light;

a first electrode provided integrally with the flexible thin film; and

a second electrode substantially fixed to the frame member so as to oppose the first electrode on an opposite side of the reflection surface, the second electrode being divided in the direction connecting the two end portions,

wherein the configuration of the reflection is controlled to a desired configuration by applying a desired voltage selectively to between the first electrode and the divided second or third electrode.

According to a fifteenth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fourteenth aspect, wherein the reflection surface of the flexible thin film is formed of metallic thin film and serves as the first electrode.

According to a sixteenth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fourteenth aspect, wherein an openings are provided on both sides of the reflection surface in the flexible member across a straight line connecting the end portions supported by the frame member.

According to a seventeenth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fourteenth aspect, wherein in a region between the end portion supported by the frame member and the reflection surface in the flexible thin film, stiffness thereof in the direction in which the second electrode is divided is decreased.

According to an eighteenth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the seventeenth aspect, wherein the region in which the stiffness of the flexible thin film is dropped is wave-like.

According to a nineteenth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the eighteenth aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and silicon nitride or metallic thin film and silicon oxide.

According to a twentieth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the seventeenth aspect, wherein as for the sectional area of the flexible thin film in a direction perpendicular to the direction in which the second electrode is divided, that of the region in which the stiffness of the flexible thin film is dropped is smaller than that of a region corresponding to the reflection surface.

According to a twenty-first aspect of the present invention, there is provided a variable geometry cylinder mirror according to the seventeenth aspect, wherein an opening or a cutout is provided in the region in which the stiffness of the flexible thin film is dropped.

According to a twenty-second aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fourteenth aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and polymer material thin film.

According to a twenty-third aspect of the present invention, there is provided a variable geometry cylinder mirror according to the twentieth aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and polymer material thin film.

According to a twenty-fourth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the twenty-first aspect, wherein the flexible thin film is composed of overlaid layers of metallic thin film and polymer material thin film.

According to a twenty-fifth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the first aspect, wherein the flexible thin film having the frame member, the reflection surface and the first electrode is manufactured by:

a diffused layer forming step of forming a diffused layer having a predetermined shape of a conductive type in a first main face of a mono-crystal silicon substrate of another conductive type;

a thin film laminating step of laminating a thin film on the first main face of the mono-crystal silicon substrate;

an etching step of, with a predetermined voltage applied to the diffused layer of the conductive type, carrying out electrochemical etching from a second main face in etching solution; and

a cutting and separating step of cutting and separating frame-like mono-crystal silicon which is part of the mono-crystal silicon substrate form portions corresponding to the flexible thin film and the frame member.

According to a twenty-sixth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fourteenth aspect, wherein the flexible thin film having the frame member, the reflection surface and the first electrode is manufactured by:

a diffused layer forming step of forming a diffused layer having a predetermined shape of a conductive type in a first main face of a mono-crystal silicon substrate of another conductive type;

a thin film laminating step of laminating a thin film on the first main face of the mono-crystal silicon substrate;

an etching step of, with a predetermined voltage applied to the diffused layer of the conductive type, carrying out electrochemical etching from a second main face in etching solution; and

cutting and separating step of cutting and separating frame-like mono-crystal silicon which is part of the mono-crystal silicon substrate form portions corresponding to the flexible thin film and the frame member.

According to a twenty-seventh aspect of the present invention, there is provided a variable geometry cylinder mirror according to the fifth aspect, wherein the flexible thin film having the frame member, the reflection surface and the first electrode is manufactured by:

a groove forming step of forming parallel grooves in a first main face of a flat substrate;

a thin film forming step of forming a thin film on the first main face of the substrate;

an etching step of etching until the thin film formed in the thin film forming step is exposed from a second main face of the substrate; and

a cutting and separating step of cutting and separating a fame-like portion which is part of the substrate from portions corresponding to the flexible thin film and the frame member.

According to a twenty-eighth aspect of the present invention, there is provided a variable geometry cylinder mirror according to the eighteenth aspect, wherein the flexible thin film having the frame member, the reflection surface and the first electrode is manufactured by:

a groove forming step of forming parallel grooves in a first main face of a flat substrate;

a thin film forming step of forming a thin film on the first main face of the substrate;

an etching step of etching until the thin film formed in the thin film forming step is exposed from a second main face of the substrate; and

a cutting and separating step of cutting and separating a fame-like portion which is part of the substrate from portions corresponding to the flexible thin film and the frame member.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiment of the invention, and together with the general description given above and the detailed description of the preferred embodiment given below, serve to explain the principles of the invention.

FIGS. 1A and 1B

are perspective views of an upper face and a lower face showing the entire structure of a variable geometry cylinder mirror according to a first embodiment of the present invention;

FIGS. 2A and 2B

are perspective views of an upper face and a lower face showing a bottom substrate

101

of the variable geometry cylinder mirror according to the first embodiment of the present invention;

FIGS. 3A and 3B

are perspective views of an upper face and a lower face showing an intermediate substrate

102

of the variable geometry cylinder mirror according to the first embodiment of the present invention;

FIGS. 4A and 4B

are perspective views of an upper face and a lower face showing a top substrate

103

of the variable geometry cylinder mirror according to the first embodiment of the present invention;

FIGS. 5A and 5B

are enlarged views taken in the direction of an arrow A and an arrow B shown in

FIG. 1A

;

FIG. 6

is a sectional view parallel to a slit-like opening portion

104

in a region in which a lower electrode

109

and an upper electrode

117

oppose each other for explaining the operation of the variable geometry cylinder mirror according to the first embodiment of the present invention;

FIG. 7

is a top view of the intermediate substrate

102

for explaining the method of manufacturing the intermediate substrate of the variable geometry cylinder mirror according to the first embodiment of the present invention;

FIGS. 8A and 8B

are a sectional view taken along the line

8

A—

8

A and a sectional view taken along the line

8

B—

8

B in

FIG. 7

;

FIGS. 9A and 9B

are a sectional view taken along the line

9

A—

9

A and a sectional view taken along the line

9

B—

9

B in

FIG. 7

;

FIGS. 10A and 10B

are a sectional view taken along the line

10

A—

10

A and a sectional view taken along the line

10

B—

10

B in

FIG. 7

;

FIGS. 11A and 11B

are perspective views of an upper face and a lower face showing an intermediate substrate

201

of a variable geometry cylinder mirror according to a second embodiment of the present invention;

FIG. 12

is a sectional view taken along the line

12

—

12

in

FIG. 11A

;

FIG. 13

is a sectional view for explaining a method of manufacturing an intermediate substrate

201

of the variable geometry cylinder mirror according to the second embodiment of the present invention;

FIG. 14

is a sectional view for explaining the method of manufacturing the intermediate substrate

201

of the variable geometry cylinder mirror according to the second embodiment of the present invention;

FIG. 15

is a sectional view for explaining the method of manufacturing the intermediate substrate

201

of the variable geometry cylinder mirror according to the second embodiment of the present invention;

FIG. 16

is a sectional view for explaining the method of manufacturing the intermediate substrate

201

of the variable geometry cylinder mirror according to the second embodiment of the present invention;

FIG. 17

is a sectional view for explaining the method of manufacturing the intermediate substrate

201

of the variable geometry cylinder mirror according to the second embodiment of the present invention;

FIG. 18

is a sectional view for explaining the method of manufacturing the intermediate substrate

201

of the variable geometry cylinder mirror according to the second embodiment of the present invention;

FIG. 19

is a sectional view for explaining the method of manufacturing the intermediate substrate

201

of the variable geometry cylinder mirror according to the second embodiment of the present invention;

FIGS. 20A and 20B

are perspective views of an upper face and a lower face showing an intermediate substrate

400

of a variable geometry cylinder mirror according to a third embodiment of the present invention;

FIGS. 21A and 21B

are perspective views of an upper face and a lower face showing a top substrate

501

of a variable geometry cylinder mirror according to a fourth embodiment of the present invention;

FIGS. 22A and 22B

are perspective views of an upper face and a lower face showing a bottom substrate

108

of a variable geometry cylinder mirror according to a fifth embodiment of the present invention;

FIGS. 23A and 22B

are perspective views of an upper face and a lower face showing a top substrate

608

of the variable geometry cylinder mirror according to a fifth embodiment of the present invention;

FIGS. 24A and 24B

are perspective views of an upper face and a lower face showing a bottom substrate

801

of a variable geometry cylinder mirror according to a sixth embodiment of the present invention;

FIGS. 25A and 25B

are enlarged views taken in the direction of an arrow A and an arrow B in

FIG. 24A

; and

FIG. 26

is a perspective view showing the main structure of a monolithic type reflection mirror unit disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402 as an example of a conventional variable geometry cylinder mirror which is deformed cylindrically.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of the invention as illustrated in the accompanying drawings, in which like reference numerals designate like or corresponding parts.

Hereinafter, the preferred embodiments of the present invention will be described with reference to the accompanying drawings.

(First Embodiment)

A variable geometry cylinder mirror according to a first embodiment of the present invention will be described with reference to

FIGS. 1A

,

1

B to

10

A,

10

B.

FIGS. 1A and 1B

are perspective views of an upper face and a lower face showing the entire structure of the variable geometry cylinder mirror according to the first embodiment of the present invention.

The variable geometry cylinder mirror is constituted of three layers: a bottom substrate

101

, an intermediate substrate

102

and an top substrate

103

, disposed with a constant space specified by each spacer.

The top substrate

103

has a slit-like opening portion

104

formed therein, for introducing light.

As evident from the same Figure, the bottom substrate

101

and the top substrate

103

are projected with respect to the intermediate substrate

102

in opposite directions.

A lower electrode pad

105

is formed on a projected portion of the bottom substrate

101

.

An upper electrode pad

106

and an intermediate electrode pad

107

are formed on a projected portion of the top substrate

103

.

FIGS. 2A and 2B

are perspective views of an upper face and a lower face showing the bottom substrate

101

.

The bottom substrate

101

is made of mono-crystal silicon substrate

108

having a thickness of 300 μm, and has a plurality of lower electrodes

109

disposed symmetrically across a region opposing the slit-like opening portion

104

formed in the top substrate

103

. The lower electrode pads

105

and connection spacers

110

have a height of 30 μm relative to the top substrate

103

.

The silicon substrate

108

has a wiring layer which connects the respective lower electrodes

109

and lower electrode pads

105

through an interlayer insulating film and contact holes (not shown).

Such multi-layer electrodes and wiring can be formed easily on the silicon substrate

108

using ordinary integrated circuit manufacturing technology.

FIGS. 3A and 3B

are perspective views of upper face and lower face showing the intermediate substrate

102

.

This intermediate substrate

102

has a flexible thin film

112

formed on a mono-crystal silicon substrate

111

having the thickness of 20 μm, the flexible thin film

112

being comprised of polyamide film 1 μm thick and Au/Cr overlaid film 50 μm thick.

The flexible thin film

112

is exposed to an opposite side of the mono-crystal substrate

111

as Au, acting as reflection faces.

A rectangular opening portion

113

and a cutout portion

114

are formed in the mono-crystal silicon substrate

111

, through which the flexible thin film

112

is exposed, the mono-crystal silicon substrate

111

being deformable with a slight stress.

Cutouts

115

are formed in the flexible thin film

112

along two side ends parallel to the slit-like opening portion

104

in the top substrate

103

, in the opening portion

113

. The flexible thin film

112

is like a belt supported by two sides perpendicular to the slit-like opening portion

104

in the top substrate

103

.

FIGS. 4A and 4B

are perspective views of an upper face and a lower face showing the top substrate

103

.

This top substrate

103

is made of a mono-crystal silicon substrate

116

having a thickness of 300 μm, a plurality of upper electrodes

117

disposed in the form of a belt symmetrically with respect to the slit-like opening portion

104

, the upper electrode pad

106

, the intermediate electrode pad

107

, an intermediate electrode lead-out electrode

118

, a connecting spacer

120

having a height of 30 μm to the bottom substrate

101

and a connecting spacer

121

having a height of 30 μm to the intermediate substrate

102

.

The silicon substrate

116

contains wiring layer (not shown) which connects the respective upper electrodes

117

, intermediate electrode lead-out electrode

118

, upper electrode pad

106

and intermediate electrode pad

107

through an interlayer insulating film and contact holes (not shown).

Such multi-layer electrodes and wiring can be formed easily on the silicon substrate

116

using ordinary integrated circuit manufacturing technology.

The slit-like opening portion

104

can be formed easily by using technology applied to ordinary MEMS device such as anisotropic etching for silicon using strong alkali solution.

Next, connection of the bottom substrate

101

, intermediate substrate

102

and top substrate

103

will be described with reference to

FIGS. 5A and 5B

.

FIGS. 5A and 5B

are enlarged views taken in the direction of arrows A and B in FIG.

1

A.

That is, in these diagrams, its vertical directions are enlarged to facilitate understanding.

The connecting spacer

110

of the bottom substrate

101

is connected with the connecting spacer

120

of the top substrate

103

.

Because the height of each of the connecting spacer

110

and connecting spacer

120

is 30 μm, the bottom substrate

101

and the top substrate

103

oppose each other with a gap of 60 μm.

The intermediate substrate

102

is connected with the top substrate

103

through the connecting spacer

121

.

The height of the connecting spacer

121

is 30 μm like the connecting spacer

110

and connecting spacer

120

.

Consequently, the flexible thin film

112

on the intermediate substrate

102

is located substantially in the middle of the gap between the bottom substrate

101

and the top substrate

103

.

Various kinds of materials can be considered as raw material for the respective connecting spacers

110

,

120

,

121

. If easiness of manufacturing is taken into account, particularly, material which can be fused with heat and patterned by photolithography method is preferred.

An Au bump

119

having the height of 40 μm formed on the intermediate electrode lead-out electrode

118

on the top substrate

103

opposes substantially the center of the rectangular opening portion

113

and cutout

114

formed in the mono-crystal silicon substrate

111

of the intermediate substrate

102

. Because the height of this Au bump

119

is slight larger than that of the connecting spacer

121

of the intermediate substrate

102

, the flexible thin film

112

is pushed up by this portion. As a result, the Au bump

119

is electrically connected to the intermediate electrode pad

107

through the intermediate electrode lead-out electrode

118

on the top substrate

103

because metallic film is exposed on the surface of the flexible thin film

112

.

At this time, the flexible thin film

112

is deformed in the region of the cutout

114

. However, the deformation of the flexible thin film

112

in the region of the cutout

114

never affects the flexible thin film

112

in the region of the opening portion

113

because the flexible thin film

112

is separated by the silicon thin plate

111

having a sufficiently higher stiffness than the flexible thin film

112

.

Because the lower electrode pad

105

and the upper electrode pad

106

correspond to the lower electrode

109

and the upper electrode

106

, respectively while the flexible thin film

112

is connected to the intermediate electrode pad

107

, if an external lead wire is connected to the electrode pads

105

,

106

,

107

so as to connect them to independent power supplies, independent voltage can be applied to each of the flexible thin film

112

, the lower electrode

109

and the upper electrode

117

.

Next, the operation of the variable geometry cylinder mirror of this embodiment will be described with reference to FIG.

6

.

FIG. 6

shows a sectional view parallel to the slit-like opening portion

104

in the region in which the lower electrode

109

and the upper electrode

117

oppose each other.

If the flexible thin film

112

, all the lower electrodes

109

and all the upper electrodes

117

are grounded, the flexible thin film

112

turns into a flat shape as indicated with dotted line in the same Figure. If a high voltage is applied to the upper electrodes

117

-

1

,

117

-

2

,

117

-

5

,

117

-

6

and the lower electrodes

109

-

3

,

109

-

4

while the flexible thin film

112

, the upper electrodes

117

-

3

,

117

-

4

and the lower electrodes

109

-

1

,

109

-

2

,

109

-

5

,

109

-

6

are grounded, the flexible thin film turns to an indicated wave-like shape.

If the voltage applied to the upper electrodes

117

-

1

,

117

-

2

is slightly higher than that applied to the upper electrodes

117

-

5

,

117

-

6

, an asymmetrical deformation shape with respect to the center can be obtained as indicated in the same Figure.

By adjusting the voltage applied to the lower electrodes

109

and the upper electrode

117

, the flexible thin film

112

can be deformed into any shape.

According to this embodiment, although no electrode for activating electrostatic force is formed just below the region of the top substrate in which the slit-like opening portion

104

is formed, its influence can be reduced to a level which can be neglected by increasing the width of the top electrode

117

and the bottom electrode

109

so as to be much larger than the width of this region.

Additionally, according to this embodiment, power consumption can be kept very low by using an electrostatic force for driving and because the structure is simple, it can be miniaturized.

Further, this embodiment enables deformation to both a concave shape and a convex shape and driving force can be controlled independently for each region opposing the electrode. Therefore, for example, the flexible thin film can be changed from the concave face to the convex face without deflecting the center of the mirror or any one point vertically by controlling the distribution of the driving force appropriately.

This feature cannot be acquired from an air pressure type variable geometry mirror.

Further, because light enters directly into the flexible thin film

112

which acts as a reflection surface through the slit-like opening portion

104

, no glass face or the like exists between incident light and the reflection surface. Thus, there is no loss of light beam, change in beam path length or deterioration of focusing performance.

Although according to this embodiment, the upper electrode

117

and the lower electrode

109

are divided substantially into six equal sections, needless to say, the number of electrodes may be changed or the electrodes may be divided unequally depending on a desired configuration or accuracy.

Next, the method of manufacturing the intermediate substrate of the variable geometry cylinder mirror of this embodiment will be described with reference to

FIGS. 7

to

10

B.

FIG. 7

shows a top view of the intermediate substrate

102

. Sections

8

A—

8

A,

9

A—

9

A and

10

A—

10

A in

FIG. 7

will be described with reference to

FIGS. 8A

,

9

A and

10

A.

Further, the sections

8

B—

8

B,

9

B—

9

B and

10

B—

10

B in

FIG. 7

will be described with reference to

FIGS. 8B

,

9

B and

10

B.

As shown in

FIGS. 8A and 8B

, an N-type impurity diffused layer

123

is formed in a P-type low density semiconductor substrate (mono-crystal semiconductor substrate)

122

.

A silicon nitride film

124

is formed on both faces of the P-type low density semiconductor substrate (mono-crystal semiconductor substrate)

122

.

An opening pattern larger than the intermediate substrate

102

is formed on the rear side of the silicon nitride film

124

.

If viewed from above, the region in which the N type impurity diffused layer

123

is formed is substantially equal to the region of the intermediate substrate

102

in which the mono-crystal silicon substrate

111

is formed.

Further, it is preferable if the silicon nitride film

124

imparts a small stress on the silicon substrate

122

, by appropriately controlling the composition of that film.

Next, a polyimide film

125

having a thickness of 1 μm and a metallic film

126

having a thickness of 0.1 μm are formed successively on the silicon nitride film

124

.

Then, the metallic film

126

is patterned.

The metallic film

126

and the polyimide film

125

are removed by patterning in the region of the cutout

115

shown in FIG.

7

.

Preferably, a very thin chrome thin film is formed between the polyimide film

125

and the metallic thin film

126

, thus adhesion of the metallic film

126

is improved.

Prior to formation of the metallic film

126

, a contact hole

127

is formed in the polyimide film

125

and the silicon nitride film

124

on the front surface, so that the metallic film

126

is electrically conductive with the N-type impurity diffused layer

123

.

Next, as shown in

FIGS. 9A and 9B

, with the front surface protected by mechanical sealing or the like, electrochemical etching is carried out with a strong alkali solution by applying a positive voltage to the metallic thin film

126

.

Because the metallic film

126

is conductive with the N-type impurity diffused layer

123

, etching is progressed in the region in which the silicon nitride film

124

on the front surface is removed by patterning until the silicon nitride film

124

on the front surface is exposed with the region of the N-type impurity diffused layer

123

left.

Next, as shown in

FIGS. 10A and 10B

, the silicon nitride film on the exposed suction face on the rear side and front side is removed by reactive ion etching from the rear side.

By cutting out the polyimide film

125

along the outer shape of the left N-type impurity diffused layer

123

according to excimer laser aberration or the like, the intermediate substrate

102

is obtained.

Although this embodiment indicates one manufacturing method of the intermediate substrate, it is needless to say that actually, a plurality of the intermediate substrates are obtained from one silicon wafer.

According to this method of manufacturing the intermediate substrate, as it can be formed in a completely monolithic way according to ordinary semiconductor manufacturing technology and MEMS technology, excellent productivity and safety are ensured.

Particularly, the manufacturing method of this embodiment in which the flexible thin film is formed on a thick solid substrate while the substrate is turned into thin film by electrochemical etching is preferable for an application requiring a high accuracy reflection surface in that there is no distortion accompanying a machining process for a frame member.

(Second Embodiment)

A second embodiment of the present invention will be described with reference to

FIGS. 11A

to

19

.

This embodiment is different from the first embodiment only in the intermediate substrate.

FIGS. 11A and 11B

are perspective views of an upper face and a lower face showing the structure of an intermediate substrate

201

of a variable geometry cylinder mirror according to the second embodiment of the present invention.

Basically, the intermediate substrate

201

of this embodiment has the same configuration as the intermediate substrate

102

of the first embodiment shown in

FIGS. 3A and 3B

. A flexible thin film

203

comprising silicon nitride film 400 nm thick and metallic thin film 50 nm thick is formed on the top face of a thin mono-crystal silicon substrate

202

having the thickness of 20 μm which serves as a frame member.

Here it is assumed that the metallic thin film is exposed to the top face.

In the same manner as in the first embodiment, a rectangular opening portion

204

and a cutout

205

are formed in the mono-crystal silicon substrate

202

and a belt-like flexible thin film

203

is exposed in this portion and deformable with a slight stress.

Like the first embodiment, in the opening portion

204

, cutouts

206

are formed in the flexible thin film

203

on its ends along two sides parallel to the slit-like opening

104

in the top substrate

103

and the flexible thin film

203

is shaped in the form of a belt supported by two sides perpendicular to the slit-like opening

104

in the top substrate

103

.

A wave-like portion

207

of the flexible thin film

203

is formed near the two sides supporting the flexible thin film

203

.

Next,

FIG. 12

shows a section taken along the line

12

—

12

in FIG.

11

A.

The flexible thin film

203

constructs the wavelike portion

207

in the vicinity of its sides supported by the thin mono-crystal silicon substrate

202

which acts as a frame member.

The variable geometry cylinder mirror of this embodiment is driven in the same manner as the variable geometry cylinder mirror of the first embodiment shown in FIG.

6

. Because both the ends of the flexible thin film

203

are constructed in the form of a wave, it is expanded or contracted easily through this portion. Thus, if material having a large longitudinal elastic modulus like silicon nitride film is utilized as the flexible thin film

203

in the variable geometry cylinder mirror of the first embodiment, a relatively large deflection can be secured even when a high voltage is not applied to the same upper electrode

117

or lower electrode

109

as in the variable geometry cylinder mirror of the first embodiment.

That is, the mechanical properties of the silicon nitride film only slightly change over time, and its stiffness remains substantially high. This embodiment is preferable for long term use in high temperature and humidity environments.

Preferably, the wave-like portion

207

is located near the end portion, away from direct light.

Although in this embodiment, the wave-like portion

207

is provided on both end portions, it is needless to say that it could be provided on one side only.

Next, a method of manufacturing the intermediate substrate

201

of the variable geometry cylinder mirror according to the second embodiment of the present invention will be described with reference to

FIGS. 13

to

16

.

A silicon nitride film is formed on both faces of an overlay type SOI substrate in which as shown in

FIG. 13

, a mono-crystal silicon active layer

303

having a thickness of 20 μm is bonded to a mono-crystal silicon substrate

301

having a face bearing of <100>, 500 μm thick through a silicon oxide film

302

.

Then, upper and rear face silicon nitride films

304

and

305

are formed by patterning.

Next, as shown in

FIG. 14

, the mono-crystal silicon active layer

303

is patterned by reactive ion etching with the upper face silicon nitride pattern

304

as a mask. Consequently, a thin silicon region corresponding to the frame member

202

is formed as shown in FIG.

12

.

Next, as shown in

FIG. 15

, an opening portion

306

is formed in the exposed silicon oxide film

302

with ordinary photolithography technology.

Next, as shown in

FIG. 16

, anisotropic etching is carried out in the opening portion

306

up to 2 μm with tetramethyl ammonium hydroxide (YMAH) with the rear face protected and the silicon oxide film

302

as a mask, so that a depression

307

is formed.

Next, as shown in

FIG. 17

, the exposed silicon oxide film

302

is removed by hydrogen fluoride acid.

Next, as shown in

FIG. 18

, a silicon nitride film

308

is formed on the top face according to the chemical vapor deposition (CVD) method.

At this time, at a portion in which the dent portion

307

is formed, the silicon nitride film

308

is turned to a wave-like portion

309

.

Next, as shown in

FIG. 19

, with the front face protected and the silicon nitride film pattern

305

as a mask, the silicon substrate

301

is etched until the silicon nitride film

308

is exposed.

After that, the thin mono-crystal silicon substrate

202

is cut out along its outer periphery as a frame member shown in FIG.

12

and the intermediate substrate

201

is formed by depositing Au/Cr thin film on an opposite side to the thin mono-crystal silicon substrate

202

of the silicon nitride film

308

.

According to the method of manufacturing the intermediate substrate of this embodiment, the stabilized fine wave-like structure can be achieved by using the ordinary MEMS technology, because steps of forming a groove in the mono-crystal silicon substrate

301

according to the photolithography technology, forming the silicon nitride film equally along this configuration and then removing the substrate after that, are adopted.

Although the active layer of the SOI substrate is used as the frame member of the intermediate substrate, a thin mono-crystal silicon forming step may be adopted by using electrochemical etching, in the same manner as in the first embodiment.

According to the method of manufacturing the intermediate substrate of this embodiment, the substrate cost is higher than the method of using electrochemical etching, and the flatness achieved on the substrate is slightly worse. However, because the step of forming the diffused layer can be omitted, the device can be produced in less time.

(Third Embodiment)

A third embodiment will be described with reference to

FIGS. 20A and 20B

. This embodiment is different from the first embodiment only in the structure of the intermediate substrate.

FIGS. 20A and 20B

are perspective views of an upper face and a lower face showing an intermediate substrate

400

of a variable geometry cylinder mirror according to the third embodiment of the present invention.

Although basically this intermediate substrate

400

has the flexible thin film

112

composed of mainly polyimide film like the first embodiment, a plurality of circular opening portions

401

are formed in the vicinity of sides supported by the thin mono-crystal silicon

111

.

This circular opening portion

401

may be formed by using a photolithography method at the same time when the cutout

115

is formed.

This method does not increase the quantity of steps, as compared to the first embodiment.

According to this embodiment, stiffness in the vicinity of the side supported side of the flexible thin film

112

is reduced by the circular opening portion

401

, so that expansion/contraction are enabled by a smaller electrostatic attracting force. As a result, the driving voltage can be reduced as compared to the first embodiment.

According to this embodiment, the plurality of circular opening portions

401

are provided to achieve low stiffness in part of the flexible thin film

112

. Needless to say, the shape of this opening portion

401

may be formed in various ways such as rectangular shape, slit, etc.

The same effect can be obtained by providing a U-like cutout or partially thinning, as well as by using a complete opening shape.

That is, by setting smaller the sectional area used for achieving low stiffness in the flexible thin film than the other portions, the stiffness may be adjusted just at a desired portion.

(Fourth Embodiment)

A fourth embodiment will be described with reference to

FIGS. 21A and 21B

.

This embodiment is different from the first embodiment only in the structure of the top substrate.

FIGS. 21A and 21B

are perspective views of an upper face and a lower face showing the structure of an upper substrate

501

according to the fourth embodiment of the present invention.

The structure of this top substrate

501

is similar to that of the top substrate

103

of the first embodiment, but different in that a quartz substrate

501

is used as the substrate and the slit-like opening portion

104

is omitted.

Because no electrode is formed in a region irradiated with incident light if the substrate is constructed of a transparent quartz, the incident light can reach the intermediate substrate having a reflection surface, without providing with any opening.

A portion indicated by dotted line in

FIGS. 21A and 21B

is a region through which light enters the flexible thin film.

That is, according to this embodiment, by forming a substrate located in the region irradiated with the incident light of transparent quartz without providing the top substrate with any opening, an optical opening can be secured.

Although in this embodiment, focusing performance is affected by an influence of distortion of the quartz substrate

501

, particularly, this embodiment does not suit to high precision applications. However it is preferable for an application demanding for reduction of cost because the manufacturing method can be simplified.

In the meantime, needless to say, any other material may be used instead of quartz as long as it allows light through it.

(Fifth Embodiment)

A fifth embodiment will be described with reference to

FIGS. 22A

,

22

B,

23

A and

23

B.

This embodiment is different from the first embodiment in the structures of the bottom substrate and the top substrate.

FIGS. 22A and 22B

are perspective views of an upper face and a lower face showing the structure of a bottom substrate

508

of a variable geometry cylinder mirror according to the fifth embodiment of the present invention.

According to the first embodiment shown in

FIGS. 2A and 2B

, no electrode is formed just below a light receiving portion while the lower electrodes

109

are disposed symmetrically on both sides of this region. However, according to this embodiment, top electrodes are formed such that the electrodes on both sides are combined.

FIGS. 23A and 23B

are perspective views of an upper face and a lower face showing the structure of a top substrate

608

of the variable geometry cylinder mirror according to a fifth embodiment of the present invention.

As for the top substrate

608

, as shown in

FIGS. 23A and 23B

, that substrate is the same transparent quartz substrate

608

same as in the fourth embodiment, the electrode is composed of a transparent ITO and the upper electrodes

602

are disposed on the light receiving portion also.

A portion indicated with dotted line in

FIGS. 23A and 23B

is a region through which light enters the flexible thin film.

In the same manner as in the fourth embodiment, this embodiment adopts a light transparent material for a substrate and electrodes which light enters and secures an optical opening in order to make light enter into the flexible thin film.

According to this embodiment, a plurality of electrodes are disposed on both faces opposing the flexible thin film on the intermediate substrate. Because the top substrate and the upper electrodes are formed of a transparent material, the electrodes can be disposed just over a light receiving portion of the top substrate.

According to this embodiment, beam path length changes depending on the position of the incident light and focusing performance deteriorate because the quartz substrate

608

and the upper electrodes

602

exist between incident light and a light receiving position. However, this is preferable for a case where the width of the incident light is large or positioning of a variable geometry mirror relative to incident light is difficult.

The problem of the above-described deterioration in focusing performance can be avoided to some extent, if, after the upper electrodes

602

are formed, the top face of the quartz substrate

608

is coated with a dielectric film having substantially the same refractivity as the upper electrodes

602

, and this film is flattened.

Although the upper and lower electrodes

602

,

601

are symmetrical to the flexible thin film on the intermediate substrate, they may be asymmetrical in the same way, as described in the first embodiment.

For example, if the upper electrode

601

is composed of a single electrode opposing the entire range of the flexible thin film on the intermediate substrate while the electrostatic attracting force applied to the divided lower electrodes is differed according on each position, the flexible thin film can be deformed unevenly.

(Sixth Embodiment)

A sixth embodiment of the present invention will be described with reference to

FIGS. 24A

,

24

B,

25

A and

25

B.

This embodiment adopts a two-layer structure by omitting the top substrate

103

of the first embodiment.

Its basic operating principle is the same as the above-described embodiment. Although it is incapable of controlling high-precision unevenness in the configuration, this embodiment is more advantageous since the number of electrodes can be reduced.

FIGS. 24A and 24B

are perspective views of an upper face and a lower face showing the structure of a lower substrate

801

of a variable geometry cylinder mirror according to the sixth embodiment of the present invention.

FIGS. 25A and 25B

are enlarged views taken in the direction of arrows A and B in

FIG. 24A

, indicating the assembly diagram of this embodiment.

These figures are represented in enlargement in the vertical direction to facilitate understanding.

Differences in terms of structure between this embodiment employing the two-layer structure and the three-layer structure of the first embodiment are as follows.

(1) Forming the intermediate substrate electrode lead-out pad on the top substrate and the Au bump formed thereon on the lower substrate.

(2) Connecting the intermediate substrate to the spacer member on the lower substrate.

Because the polyimide film side is joined to the spacer on the lower substrate, the installation direction is reverse to the three-layer structure.

(3) Thus, the Au thin film needs to be deposited on the side of the thin mono-crystal silicon substrate of the intermediate substrate as a reflection surface.

Thus, as described above, the present invention can provide a small variable geometry cylinder mirror which can be changed to a free configuration including an asymmetrical one.

Further, the present invention is capable of providing a variable geometry cylinder mirror which can be changed continuously from the concave face to the convex face and further which can be deformed with the center or any point in its reflection mirror portion fixed.

Further, the present invention can provide a variable geometry cylinder mirror which can obtain large changes in curvature with a relatively low voltage.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Number	Name	Date	Kind
4615595	Hornbeck	Oct 1986	A
4710732	Hornbeck	Dec 1987	A
5115292	Takebe et al.	May 1992	A
5447600	Webb	Sep 1995	A
5512374	Wallace et al.	Apr 1996	A
5585956	Lee et al.	Dec 1996	A
6147789	Gelbart	Nov 2000	A

Variable geometry mirror having high-precision, high geometry controllability

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

CROSS-REFERENCE TO RELATED APPLICATIONS

US Referenced Citations (7)

Foreign Referenced Citations (1)